Processing insert, and production of same

ABSTRACT

The invention pertains to a processing insert comprised of a body with a hard metal or ceramic substrate and with a multilayer coating and the manufacture of same. In order to have a highly fracture-tough insert with a relatively thick coating, it is suggested that an external layer (protective layer) be applied according to the CVD process, said layer being either a monophase or multiphase layer of Zr-based or Hf-based carbide nitride or carbonitride, and presenting internal compressive stresses. The layer(s) underlying the external layer, also applied according to the CVD process, also present(s), without any exception, internal compressive stresses, while at least one of them, maybe the only one laying under the protective layer is made of TiN, TiC and/or TiCN. The coating is applied according to a continuous CVD process at temperatures of 900° C. to 1100° C. and involves a specific modification of the gas compounds.

CROSS REFERENCE TO RELATED APPLICATIONS

This applications is a national stage of PCT/DE98/01237 filed May 2,1998 and based upon German national application 197 19 195.9 of May 9,1997 under the International Convention.

FIELD OF THE INVENTION

The invention relates to a cutting insert for machining operations,consisting of a hard metal, cermet or ceramic substrate body with amultilayer coating.

BACKGROUND OF THE INVENTION

Substrate bodies coated with a hard materials, optionally also coatedwith multiple layers, are known to the state of the art. As a rule thehard-material coating serves for creating a wear-resistant surfacelayer, which is combined with tough substrate bodies mechanicallycapable to bear high loads. According to the state of the art, twodifferent methods are used, so-called chemical vapor deposition (CVD) orthe physical vapor deposition (PVD). The usual protective layers consistfor instance of TiC, TiN and/or aluminum oxide. It has also beenproposed to apply multiple layer coatings with the layer sequence TiN,Ti(C,N), Ti(C,N), TiN on a substrate body mit any desired C:N mixingratios.

From DE 195 30 517 also metal carbonitride hard materials on a substratebody are known, wherein the metal of the metal carbonitride layercontains two or more of the elements of the group Ti, Zr, Hf, V, Nb, Ta,Cr, Mo and W. The layer is described particularly as a quaternary layerof (Ti,Zr)(C,N) obtained through CVD. As a special embodiment examplefor an indexable insert, a coating consisting of an approximately 1 μmthick TiN layer, a 8 μm thick (Ti,Zr)(C,N) layer and a last layer with athickness between 3 and 5 μm of Al₂O₃ was deposited on a hard metalsubstrate body.

The already mentioned PVD coatings, which can be already producedstarting from approximately 400° C., are used especially fortemperature-sensitive substrate bodies, particularly for the coating ofrapid machining steel, which during coating should not be subjected tohigh temperatures.

The references WO 92/05296 or U.S. Pat. No. 5,143,488 with a similarcontent indicate in addition that TiN layers deposited through the CVDprocess show tensile strains, while TiN coatings applied through the PVDprocess show compressive strains which do not lead to fracture as is thecase with tensile strains. In order to improve the fracture resistance,these references propose to combine one or more CVD-layers with one ormore layers deposited through PVD. As materials for the inner layerdeposited by CVD, nitrides of titanium, hafnium and/or zirconium areproposed, and for the layers deposited by PVD nitrides and carbonitridesof the mentioned metals are proposed. From the point of view of processtechnology, there is a disadvantage in that two successive, relativelyexpensive, different coatings (CVD, PVD) have to be applied by means ofdifferent apparatus. Furthermore it has been found that the multilayercoating consisting of inner coatings deposited through CVD and at leastone outer layer deposited through PVD tend to detach themselves fromeach other in case of thicker layers.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to avoid theaforementioned drawbacks. The cutting insert should have a high fractureresistance (bending strength). The process required for its manufactureshould be cost-effective and performed with the minimum possibleequipment expenditure.

A cutting insert for machining operations can consist of a cermet orceramic substrate body with a multilayer coating, whose outer layer(cover layer) consists of a single-phase or multiphase layer ofcarbides, nitrides or carbonitrides on a Zr or Hf basis, which wasapplied by means of CVD and presents inner compressive strains. Itsunderlying layers applied also by CVD have exclusively inner tensilestrains, whereby at least one or the sole underlying layer consists ofTiN, TiC and/or Ti (C,N).

SUMMARY OF THE INVENTION

The multilayer coating on a hard metal, cermet or ceramic substrate bodyhas an outer layer (cover layer) consisting of a multiple phase layer ofcarbides, nitrides or carbonitrides on a zirconium or hafnium basis andwhich has inner compressive strain. The underlying layer or layers,without exception, have tensile stresses, whereby at least one or thesole underlying layer consists of titanium nitride, titanium carbideand/or titanium carbonitride. All layers are applied by CVD, wherebyalso such embodiments are included wherein the cover layer can consistof several individual layers of the same or of a different materialcomposition. It is essential for the present invention that the coverlayer contain zirconium or hafnium which can be in the form of acarbide, nitride or carbonitride and can be combined with an underlyinglayer of a titanium carbide, nitride and/or carbonitride. Preferably thecompressive strains range between −500 to −2500 MPa (compressive strainsare defined with negative values in contrast to tensile strains whichare defined with positive values).

As a single-phase cover layer a carbide, nitride or carbonitride ofzirconium or hafnium can be selected. Alternatively thereto, there arealso single-phase cover layers consisting of a carbide, nitride orcarbonitride of the form (M₁,M₂) (C_(x)N_(1−X)) with M₁=Zr or Hf andM₂=Ti, Hf, Nb, whereby 0≦x≦1. In the latter case they are also definedas so-called quaternary multimetal carbonitrides.

A preferred two-phase outer layer consists of a carbide, nitride orcarbonitride of zirconium or hafnium and ZrO₂. ZrO₂ can be present inmonocline, tetragonal and/or cubic modification. Particularly the outerlayer can contain a composition of the form Me(C_(x)N_(1−x)) with Me=Zror Hf and 0.3≦x≦7. If the cover layer is a single phase layer, then itdiffers from the two-phase layer in that it has a uniform structure andlattice constant, which includes particularly tertiary and quaternarycarbides, nitrides or carbonitrides, wherein zirconium or hafnium mustbe present either alone or together for at least 50% by atom. Therespective metal atoms then distribute themselves statistically on asublattice, while their metalloids, carbon and nitrogen are alsorandomly distributed on the other sublattice.

In a two-phase layer, which consists particularly of a carbide nitrideor carbonitride of zirconium or hafnium, in addition also containingZrO₂, two phases, which are different as to their crystalline structureand lattice, coexist next to each other. The second phase ZrO₂ amountspreferably to a proportion between 15 and 60% by mass.

According to a further embodiment of the invention, between the coverlayer and at least one layer close to the substrate body, one of thelower layers can consist of Al₂O₃.

Preferred thicknesses of the cover layer range between 2 μm and amaximum of 10 μm, whereby further preferably the total thickness of theinner layers subject to tensile strains and the outer layers subject tocompressive strains ranges between 5 μm and 25 μm, particularly between10 and 20 μm.

Preferably a first TiN-layer with a thickness up to 2 μm and one or moreTiCN-layers of up to 5 μm are deposited on the substrate body, on whicha single-phase or two-phase cover layer with a thickness of up to 5 μmhas been deposited.

For the production of a cutting insert of the aforementioned kind thecoating is performed in an uninterrupted CVD process at temperaturesbetween 900° C. and 1100° C. through respective changes of the gascomposition.

The compressive strain of an outer layer of a single-phase multimetalcarbonitride can be increased particularly due to the fact that afterthe CVD deposition follows a heat treatment at a temperature higher thanthe substrate body temperature during the last deposition. Therespective temperatures lie between 95° C. and below the eutectictemperature of the substrate body material. The heat treatment lasts atleast for 15 minutes, so that a spinodal segregation into atitanium-rich and a zirconium-rich phase takes place.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph illustrating the invention.

SPECIFIC DESCRIPTION AND EXAMPLES

Advantageously, After the conclusion of the CVD process, the coating isadditionally subjected to a mechanical surface-smoothing treatment, bymeans of abrasive brushes or of dry or wet blasting with fine blastingagents, preferably glass balls or corundum.

In CVD tests various coatings were applied to indexable inserts made ofhard metal as shown in Table 1. In this coatings through a measuringmethod with X-rays (so-called sin²ψ=method) the strains in the layerbordering the cover layer have been measured. For comparison in theTable 1 also measured values of TiN and TiC layers applied through PVDare shown (see Examples 1 is and 2). These layers applied through PVDshow the inherent high compressive strains known from the prior art,while the TiN, TiC and Ti(C,N) layers applied through CVD according toExamples 3 to show different high tensile strains, which is also knownfrom the state of the art. By contrast in Examples 6 to 8 coatingsaccording to the invention are shown, namely respectively an inner layerof Ti(C,N) and a cover layer of Zr(C_(0.49)N_(0.51)) (Example

We claim:
 1. A cutting insert for machining operations consistingessentially of a cermet or ceramic substrate body with a multilayercoating having an outer cover layer consisting of a single-phase ormultiphase layer of Hf or Zr carbides, nitrides or carbonitrides appliedby means of CVD providing inner compressive strains, and at least oneunderlying layer such that any underlying layer is applied also by CVDand has exclusively inner tensile strains, at least one underlying layerconsisting of a material selected from the group which consists of TiN,TiC and Ti(C,N) or mixtures thereof, the strain relationship of saidlayers being such that of said layers only said outer cover layer hasinternal compressive strain and all of the others of said layers haveinternal tensile strain.
 2. The cutting insert according to claim 1wherein the outer layer is single phase and consists of a carbide,nitride or carbonitride of the form (M₁,M₂) (C_(x)N_(1−x)) with M₁=Zr orHf and M₂=Ti, Hf, Nb and 0≦x ≦1.
 3. The cutting insert according toclaim 1 wherein the outer layer is a two-phase layer consisting of acarbide, nitride or carbonitride of Zr or Hf as a first phase and ZrO₂as a second phase.
 4. The cutting insert according to claim 1 whereinthe outer layer contains ZrO₂ as a second phase in an amount of 15 and60% by mass of the outer layer.
 5. The cutting insert according to claim1 wherein the cover layer has a thickness of at least 2 μm and a maximumof 10 μm.
 6. The cutting insert according to claim 1 which has a layersequence deposited on said substrate body of TiN with a thickness up to2 μm, TiCN with a thickness up to 5 μm and a single-phase or two-phasecover layer with a thickness of up to 5 μm.
 7. The cutting insert formachining operations consisting of a hard metal substrate body with amultilayer coating whose outer cover layer consists of a single-phase ormultiphase layer of Zr or Hf carbides, nitrides or carbonitrides appliedby CVD and providing inner compressive strain, and at least oneunderlying layer applied by CVD exclusively with tensile strains,including at least one underlying layer consisting of TiN, TiC and/orTi(C,N), and a layer between the cover layer and at least one layerclose to the substrate body consisting of A1₂₀ ₃, the strainrelationship of said layers being such that of said layers only saidouter cover layer has internal compressive strain and all of the othersof said layers have internal tensile strain.
 8. The cutting insertaccording to claim 7 wherein the outer layer contains the compositionMe(C_(x)N_(1−x)) with Me=Zr or Hf and 0.3≦x ≦7.
 9. The cutting insertaccording to claim 7 wherein the total thickness of all inner layershaving tensile strains and of the outer layer with compressive strainranges between 5 and 25 μm.
 10. The cutting insert defined in claim 9wherein the total thickness is 10 to 20 μm.
 11. A method for producing acutting insert according to claim 1 wherein the coating is appliedthrough an uninterrupted CVD process at temperatures between 900° C. and1100° C., by respectively changing the gas composition.
 12. The methoddefined in claim 11 wherein after the deposition of the outer layer,this layer is subjected to a heat treatment above the last CVDdeposition temperature and below the eutectic temperature of thesubstrate body for at least 15 minutes, whereby a spinodal segregationtakes place.
 13. The method defined in claim 12 wherein the heattreatment between 1000° C. and 1200° C. takes place in a protective-gasatmosphere.
 14. The method defined in claim 11 wherein after theconclusion of the CVD process, the cover layer is subjected to anadditional mechanical smoothing treatment by means of abrasive brushesor by dry or wet blasting with fine blasting agents in the form of glassballs or corundum.